qapi: keep names in 'CpuInstanceProperties' in sync with struct CPUCore

qapi: keep names in 'CpuInstanceProperties' in sync with struct CPUCore

struct CPUCore uses 'id' suffix in the property name. As docs for
query-hotpluggable-cpus state that the cpu core properties should be
passed back to device_add by management in case new members are added
and thus the names for the fields should be kept in sync.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
[dwg: Removed a duplicated word in comment]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>